Nickel(II)-SNS Thiolate Complexes: Reactivity and Solution Dynamics

Nickel coordination chemistry with a biomimetic thiolate-imine-thioether SNSMe ligand is accompanied by diverse reactivity and multidentate ligand dynamics. Reaction of Ni(acac)(2) with 2 equiv of 2-(methylthio)-phenyl-benzothiazolidine (MPB) affords the bis(arylimino-phenylene-thiolate) complex Ni(kappa(2)-SNSMe)(2) (1; acac = acetylacetonate). Thermolysis of 1 in refluxing toluene is accompanied by imine C-C bond formation, yielding [Ni(N2S2)] (2) with a redox-active ligand. Protonation of 1 with NHTf2 at a low temperature released 1 equiv of MPB, yielding crystals of the dimeric dication {[Ni(mu-kappa(3)-SNSMe)](2)}(NTf2)(2) (3; Tf = SO2CF3) in high yield. In contrast, the same reaction at room temperature gave also paramagnetic complexes {Ni[mu-Ni(kappa(3)-SNSMe)(2)](2)}(NTf2)(2) (4) and {Ni[mu-Ni(kappa(3)-SNSMe)(2)](3)}(NTf2)(2) (5) that feature coordination of two or three pseudo-octahedral, paramagnetic Ni(kappa(3)-SNSMe)(2) units to a central Ni(II) dication via thiolate bridges. Remarkably, dissolution of 3 in a variety of solvents, including weakly coordinating CH2Cl2, rapidly generates a mixture of 4 and Ni(NTf)(2). Treatment of this mixture with Lewis bases L gave high yields of dimers {[Ni(mu-kappa(3)-SNSMe)L](2)}(NTf2)(2) for L = CNXylyl (6a) and {[Ni(mu-kappa(3)-SNSMe)]2(mu-dmpm)}(NTf2)(2) (6b; dmpm = bis(dimethylphosphino)methane) or monomers [Ni(kappa(3)-SNSMe)L](NTf2) for L = PMe3 (7a) and P(OMe)(3) (7b). Addition of 2 equiv of the strong donor N-heterocyclic carbene ligand, IPr, to 3, however, led to thioether demethylation, affording neutral dithiolate complex Ni(kappa(3)-SNS)(IPr) (8). Reaction products were characterized by NMR and mass spectrometry and complexes 1-5, 6a, 6b, 7a, and 8 by single-crystal X-ray diffraction.

Automated summary

Nickel coordination chemistry with a biomimetic thiolate-imine-thioether SNSMe ligand exhibits diverse reactivity and multidentate ligand dynamics. Reactions of the ligands with nickel at different temperatures result in the formation of complexes with varying magnetic properties.